The subject of today’s review is the white label Amperex (USA) 7308 dual triode.  Specifically, a JAN 7308 (1966 vintage) used as the input tube in my conrad-johnson Premier 140 amplifier and a set of six USN-CEP 7308 (manufactured between 1963 and 1965) that were used in my Premier 16LS2 preamplifier.   

These tubes are available at such online vendors as Upscale Audio where they retail for between $50 to $80 apiece, depending upon grade.  With all due respect, I happen to disagree with Kevin Deal’s assertion that all the variants of the Amperex 7308 sound alike but ultimately, it’s how they sound to you that matters.

Amperex (USA) 7308 White Label Line-Up                                                Amperex (USA) JAN 7308                  
      

Amperex USN-CEP 7308                                                                        Amperex USN-CEP 7308 Rear View
     

Large O-Ring Getter                                                                             Etched "418" Code
          

The reader is directed to the installments on the Amperex JAN 7308 Green Label for a review of a later version of this tube and to the Tesla PCC88 review for some information on the tubes which immediately preceded these white label Amperex 7308s. 

The output tubes used in the Premier 140 during this review were triple getter, black plate Tung-Sol 6550.  Arguably, about as good as you can get in the 6550 family.

Listening Impressions:

• Typical Amperex smoothness and musicality from the people who introduced the 6DJ8 family of tubes.
• Transient response is not quite as sharp as the Tungsram PCC88 but the treble is still well-extended.
• Inner detail/timbre is reference level and notes decay into the noise floor.
• Images are denser than the Tungsram and the sound stage extends from behind the speaker plane to the listening seat.
• Dynamics, both micro and macro, are excellent.
• Voices are more natural sounding than the Tungsram PCC88.
• Bass is solid but not as taut as the Tungsram.

Overall, there was a synergy taking place that produced a sound that was about as good as I’ve heard from my system in its present configuration.

NB:  This will most likely be the last installment centered around the Premier 16LS2 and 140 as I’ve purchased a conrad-johnson CA200 integrated amplifier and will be using it in their place.  For how long remains to be seen.

The fuses have been in situ for 45 hours playing time and were initially placed in both QUAD 989 speakers so that the writing on them could be read in a typical left-to-right fashion (this would be with the logo’s arrow pointing to the right – final photo on HiFi-Tuning Supreme Fuse, Part 2).  The interested reader should see my entry on Fuse Directionality for some background information regarding the importance, in my opinion, of properly orienting fuses in order to maximize sound quality.

Settle-/Burn-In:  Right Direction Orientation

During the course of the first day, there was a decided change in the effect the Supreme fuses had on the sound coming from my speakers.  As playing time increased, so did the clarity:  low level details became slightly more apparent, especially at reduced volume levels.  I believe this was due to an improvement in dynamics which manifested itself as superior resolution.

Listening to the first disc of American Acoustic, which I’ve copied onto my personal computer and then played wirelessly via the Oppo BDP-95, transients were sharper and note decay was longer compared to the stock fuses.  I could more clearly hear the vibration of guitar strings and during the first few hours of playing time, as the fuses settled-in, this effect became more apparent.

Vocals and spoken voice were more solid and emotive and will be discussed in further detail later.

Treble response was superior to the stock glass fuses and such things as clinking glasses and the sound of a piano was more realistic.

Total playing time over two days at this point was 13 hours.  I then flipped the fuses around so that the arrow on the logo was now pointing to the left and the writing on the fuses was upside-down.

Left Direction Orientation

Listening to Loreena McKennitt’s The Mask and Mirror, it was immediately apparent that the sound stage was deeper than I’d ever heard before.  Replay of American Acoustic revealed even sharper transients and additional detail that has previously been buried in the mix, even with the Supreme fuse in its right-facing direction in play. 

Dynamics, which had improved when introducing the Supreme fuses, were more prominent in the left-facing orientation.  Interestingly, this wasn’t a heavy-handed, across the board change in dynamics.  Rather, sounds would change volume and then return to their previous level as the audio mix dictated in a totally natural way.  This “popping” in and out continued to become more prevalent as playing time increased and never seemed forced or artificial.

Mouth noises were more distinct with the difference being subtle but definite.  Frequency extremes were handled more ably with better extension.

I noticed that I’d stopped taking notes and was just watching and listening to a movie on cable.  That’s always been a very good indication to me that the system is performing well.

The fuses were in the left-facing orientation for 21 hours (therefore, 34 hours total time since the introduction of the Supreme fuses).  At this point I flipped them once again to their original right-facing direction to determine whether what I was hearing was due to burn-in and/or orientation.

Right Direction Orientation Redux

Once the fuses were back in their original position I immediately noticed that the quality of the midrange had changed: it was more prominent.

During the 10 hours (44 hours total) they remained in this position, the fuses changed character (for the positive) as they settled-in and further burn-in occurred.  Overall, however, the presentation was not as detailed as the left-facing orientation nor was transient response and sound-staging as good.  Dynamics were also diminished and the “popping” phenomenon ceased.  They were still, in my opinion, superior to the stock glass fuses even being in the non-preferred position.

Left Direction Orientation Redux

Once the fuses were back in what I felt was the preferred position, the first thing I noticed, once again, was a change in the quality of the midrange:  it was less “rich”.  Additionally, the system had more presence, more high frequency energy, overall volume seemed diminished but dynamics were restored as if the signal were less compressed.  Inner detail was better, and the system just sounded better, period.

Conclusion

So, what did I learn?  First, the HiFi-Tuning fuses continue to be superior to stock fuses in the three applications in which they’ve been tried:  Modwright/Music Hall CD-25 (Supreme), conrad-johnson Premier 140 power amplifier (Gold), and the QUAD 989 speakers (Supreme).  Second, in my opinion, fuse orientation is as important with the HiFi-Tuning fuses as is their introduction itself into my system. 

Some listeners may actually prefer the “improper” orientation.  In those cases where richness of sound is sought over a more marked increase in detail and dynamics, a user may want to have them in this orientation.  That has not been my preference, but these after-market fuses allow for experimentation and what ultimately appeals more to you remains, as always, a personal choice.  

The subject tubes are PCC88/7DJ8 dual triodes from the Tesla Rožnov n.p. Závod Vrchlabí plant and were produced in 1965 (the six used in the Premier 16LS2) and 1966 (the single tube used as input for the Premier 140), in what was then Czechoslovakia.  They were purchased from the online vendor Tube Monger at a cost of $50 per pair.  According to Tube Monger, these are supposed to be superior to later production PCC88 with the 37 factory code from the Trinec plant.

The Tesla PCC88 replaced Telefunken (manufactured by Siemens) PCC88 tubes in both the Premier 16LS2 and 140.  Output tubes were 1960 vintage Tung-Sol 6550 black plates with triple getter construction (see this review of the earliest production top-getter only Tung-Sol 6550 black plate) and Sovtek 6H30π-DR phase splitters in the Premier 140.

Tesla PCC88 Line-Up                                                                            Tesla PCC88 Front View
     

Tesla PCC88 Rear View                                                                         Tesla PCC88 Close-Up
     

Tesla PCC88 Thick Getter Ring
    

Listening Impressions:

• Frequency response is evenly balanced and leans more to the German side (Siemens and Telefunken) of the spectrum than the Dutch (Philips/Amperex).
• Bass is solid but never draws undue attention to itself.
• Midrange is clear if a little lean making dialogue easy to understand.
• Detail is excellent with a crisp transient response.
• Upper treble is extended and airy.
• Dynamics are top-notch and the overall presentation is quick, peppy, and sparkly.
• Not as grainless as the best (Amperex, Telefunken and Siemens).
• Soundstage is wide, well-layered and populated with larger, slightly more diffuse images.
• When the recording allows, such as Vivaldi’s L'estro Armonico, Op. 3, Vol. 1: Concertos No. 1-6  DVD-A, the venue’s ambience is nicely captured.

Overall, I find the Tesla PCC88 an excellent performer and would make an especially good choice if your system tends to be a little on the dark side.

This marks my third foray into to the world of after-market premium fuses.  My previous two tries from HiFi-Tuning were the Gold 38mm Special used in my conrad-johnson Premier 140 power amplifier and the Supreme for my Modwright/Music Hall CD-25 CDP.  Both were an unqualified success, in my opinion.

So, since I’ve tried them in both a source component and an amplifier, let’s look at the end of the food chain:  speakers.  My reference speakers for nine years now have been the QUAD ESL-989 model.  They’re not perfect, but they suit my needs, and with any luck, will outlast me. 

According to a Stereophile review on the 989’s posted in November, 2002:

“Like other electrostatic loudspeakers, the ESL-989 must be plugged into AC mains to charge the diaphragms. Operating them without plugging them in can damage them. A 6VA, 100mA fuse sits in the AC socket on the speaker's rear panel next to its On/Off switch and power-on LED. The step-up transformers also have fuses, to protect the speaker's internal power supply from extreme voltage surges. Replacing these fuses involves removing the cover of the power supply.”   

That last sentence is the reason why I’ve only replaced the relatively easy to access fuses positioned on the outside of the speakers.

In today’s installment, we’ll be introduced to these little devils and a future posting will address their impact on the system’s sound quality.  My initial bias is that since these fuses follow last in the sonic transmission chain, their effects will be lesser in nature than those that are earlier.

Solo                                                                                                   At Rest
     

Close to Home                                                                                    Together with Big Brother
     

This is Where They Belong                                                                    Original Plus Spare
     

In Its New Home

Stay tuned.

The Amperex Pinched-Waist 6922 PQ has been and continues to be my favorite input tube for the conrad-johnson Premier 140 power amplifier.  This particular tube was manufactured at the Hicksville, NY plant in November, 1958 (7LK *8K ) and was packaged the 14th week of 1959.  The Amperex 6922 has the number “848” etched vertically at its top and this may indicate the tube was manufactured in the 48^th week of 1958 but that’s only guesswork on my part.

This tube has the D-getter structure and the famous pinched-waist which may be seen as a narrowing of the glass bottle starting at the splatter shield and descending to almost the middle of the plate structure.  It is thought that the narrowing was an attempt by the maker to minimize microphonics by more securely anchoring the tube’s innards.  At least one online vendor (Upscale Audio) believes that this pinched-waist version of the tube tends to be noisy.  Another vendor (Tube World) deems the 1958 Holland made version of this tube to be the best sounding 6922 ever.  You pays your money and you takes your choice.  

Amperex Pinched-Waist 6922 PQ Front View                                            Amperex Pinched-Waist 6922 PQ Shield View
     

Amperex Pinched-Waist 6922 PQ Packing Date                                         Amperex Pinched-Waist 6922 PQ D-Getter
      

Unfortunately, it is the only one of its kind that I own, so I’ve only been able to use it in my power amp.  I own two Amperex Bugle Boy 6DJ8/ECC88, also with the early D-getter structure.  One was made in July, 1958 and the other in January, 1959 and they’re from the Heerlen, Holland plant.  They are the earliest examples of this type that I have and may be the subject of a future review.    

I’ve rolled this tube into the Premier 140 many times since its capacitors were upgraded to the CJD Teflon type.  It’s been used in conjunction with many power tubes and with a variety of dual triodes in the Premier 16LS2 preamplifier.  The Listening Impressions immediately below are a compilation of my thoughts on the Amperex Pinched-Waist 6922 PQ.

Listening Impressions:

• May not have as much gain as the 6922EH. 
• Treble is softer, not as piercing with less sharp transients but the leading edge/timbre/decay cycle is of one piece and, to use a cliché, has an organic quality that is approached by other dual triodes, but never matched.
• The antithesis of “hi-fi sounding” with vocals residing more in the throat and vibrato clearly defined.
• Extended at both frequency extremes.
• Upper bass and lower midrange is somewhat emphasized.   
• Wind instruments have a breathy quality at times.
• Dynamic when the source material allows.
• The sound stage is transparent and subtly layered with each image spread across a wide, deep and tall acoustic space. 
• Percussion is reproduced, in particular, in a natural, but never edgy fashion.
• Detail retrieval is reference level and changes in the system are immediately apparent.
• Grain-free with any texture heard originating in the recording or source component.

To sum it all up in three words:  revealing, refined, musical.

The subject tube under review is a GE 6922 with an A-frame getter structure.  The tube is a bit of an anomaly for three reasons:

1. Although the getter structure is an A-frame with a dimpled disc, this is the first 6922 I’ve ever come across that’s had an A-frame.  This getter type is typically found on 6DJ8/ECC88 dual triodes.  This has sparked a bit of a controversy on Audio Asylum as to whether it might be a 6DJ8 tube that’s had its pins painted gold after the fact.
2. It’s also been suggested that it may have been made by Siemens.
3. The country of origin is also unclear.  Although the GE 6922 is marked as being made in Great Britain, the manufacturer’s code seems to indicate it was made at the Amperex Heerlen, Holland plant.

These open questions aside, I am working under the impression it is, in fact, an Amperex Holland sourced 6922 and was relabeled by/for GE.  According to the manufacturer’s code (Δ2H3), the tube was made in the third week of August, 1972.

GE 6922 A-frame                                                                                  Dimpled Disc Getter
      

Seamed Top                                                                                        Number "56" Molded Into Bottom
     

The GE 6922 replaced an Amperex pinched waist 6922 PQ as the input tube in my Premier 140 power amp.  The rest of the tube complement in the 140 was comprised of a pair of Sovtek 6H30π-DR phase splitters and an octet of New Sensor Tung-Sol 6550s; six Amperex (Holland) small halo, 1963 vintage 6DJ8s, that were marked Hewlett-Packard, were used in the Premier 16LS2 preamp.    

Listening Impressions:

• The overall sound was similar to the Amperex pinched waist 6922 PQ with a touch more energy in the mid-bass.
• Percussion, although excellent, falls just short of the much vaunted pinched waist Amperex 6922.
• Inner detail/timbre is near or at reference level.
• The sound stage is wide, deep and tall; extending to the listening position depending upon the source material.

All in all, the GE 6922 A-frame, no matter its origin, acquitted itself admirably and if you can find it, is worth a try.

Today’s installment covers the Genalex KT88 output tube.  The reader is directed to my original posting on these tubes, when used in my Premier 11A, for information regarding their physical construction and initial listening impressions. 

The Genalex KT88s in this review were used in the Premier 140 power amplifier which passed the 1,000 hour mark, since its upgrade, during their audition.  At this point in time, the CJD capacitors that were installed in the 140 should be fully broken-in.  Other tubes used in conjunction with the review set were Telefunken PCC88s in the Premier 16LS2 preamp and as the input tube for the 140 (I now have a complete set of seven) plus the Sovtek 6H30π-DR phase splitters, also in the Premier 140. 

The review set were comprised of one quad of Genalex Gold Monarchs and a quad of Genalex KT88s.  The tubes are essentially identical with the only difference being that the Gold Monarchs were intended for sale in the United States while the latter were marketed elsewhere.

Genalex Gold Monarch KT88                                                                   Review Set
     

Genalex KT88                                                                                      Genalex KT88
     

The Genalex KT88s replaced the SED 6550C power tubes and my comments below are relative to their differences.

Listening Impressions

• The increased power capability (42 watts dissipation for the KT88 versus 35 watts for the 6550C) is immediately apparent with a louder presentation at equal volume settings and a more powerful bass response with greater overall dynamics.  As a result, the music has a more solid foundation.
• Slapped percussion is more realistic although with less transient snap.  Transients are detailed but not as sharp as with the SED 6550C.
• Midrange is harmonically richer and voices are more chesty.
• There is less sparkle in the mid- to upper-treble.  However, chimes, church bells and the like are extremely realistic and reminiscent of the GE 6550A in this regard.
• The sound stage is populated with denser images that are well-layered.  

I continue to be very impressed with the Genalex KT88 and these are most definitely a top tier power tube.  Although extremely expensive in today’s market, they reward the listener with a presentation that is natural and always at the service of the music.  The changes in the resolution of the Premier 140, especially with its fully formed caps, highlight this tube’s capabilities.   

The review sample was purchased from an E-bay online store for about $20 - $25 apiece, on average.  Although not NOS, they usually scored in the 90% to above 100% range.  I find it impossible to read GE date codes, when they’re available, but assume these were made during the 1960s in their Owensboro, KY plant (the 188-5 plant code is evident on some of them).

General Electric used a process during manufacture where a grey coating was sprayed on the inside of the tube which was thought to help in shielding the tube from radio frequency interference.  They are also referred to as “smoked glass”.  The GE 6DJ8 uses a disc-type getter structure.  

GE Grey Glass 6DJ8                                                                              Line-Up 
     

Close-Up                                                                                             Bottom View
     

Disc Getter

 I’ve used the GE 6DJ8 as both the input tube for the Premier 140 amplifier in conjunction with GE 6550A and SED 6550C output tubes and in the Premier 16LS2 preamp.

Listening Impressions:

• Bass is well-developed if a little prominent and plummy at times.
• Rich midrange that’s renders voices beautifully.
• Delicate treble although slightly rolled-off in comparison to some others, such as the Lorenz PCC88.
• Very good timbre and decay.  Piano is especially well-rendered.
• Dense images populating a well laid-out sound stage.  Roger Waters 1992 disc Amused to Death puts you in the midst of a sonic diorama.
• Although detail is excellent, it’s not reference level but you don’t mind because they’re so musical sounding.

Although the GE 6DJ8 may be a cut below, if you’re looking to get a taste of the vintage Amperex 6DJ8 sound, these are a low cost alternative.   

The review set of Valvo 6922 dual triodes is a mixed bag:  three of them were manufactured in Germany, one by Amperex in Hamburg and the other two by Siemens in Munich; the remaining four were produced in the Amperex Heerlen, Holland plant.  The vintages also vary:  three were made in 1964, one in 1969 and the remaining three in 1970.

In addition, five of the tubes bear a red Valvo label while the remaining pair (both 1970 Heerlen-made) is white label.  The red label group was most likely destined for industrial use while the much more common white pair for consumer consumption.

Valvo 6922 at Work in Premier 16LS2                                                      Valvo 6922 (Amperex, Hamburg)
      

Valvo 6922 (Amperex, Heerlen)                                                              Valvo 6922 (Amperex, Heerlen)                                                

Valvo 6922 (Heerlen) Close-Up                                                               Valvo 6922 Getter Support (Amperex and Siemens)
     

Valvo 6922 Heerlen 1964 Date Code

The Valvo 6922’s replaced a set of seven Amperex 6922 PQ (USA) tubes with the large O-ring getter.  During the course of break-in, their sound did change at around the 10 hour mark.  They were initially somewhat bass-shy and the midrange had a hollow quality.  Both of these characteristics disappeared as the New Old Stock (NOS) tubes burned-in.

Listening Impressions:

• Transients are sharper with a more clearly delineated timbre when listening to the 20-bit mastered American Acoustic CD (disc 1).  Strummed acoustic guitar is precise and delicate while fingers sliding across guitar strings are clearly heard.
• Decay is long even though the music is quick and sprightly. 
• Detail is first-rate on the Teldec recording of Vivaldi’s The Four Seasons with Nikolaus Harnoncourt conducting the Concentus musicus Wien.  When this disc is played via the Oppo BDP-95, the cabling is purely XLO Signature straight through to the speakers (1.1 IC => 1.1 IC => 5.1 SC) and there is a purity of tone and clarity of detail that’s like an open doorway to the music’s venue.  The greater richness of tone is clearly evident on this transcription using contemporary instrumentation when compared to the equally excellent, period-instrument rendition on Archiv by Trevor Pinnock leading The English Concert.     
• The oboe solo on “Prairie Lullaby” from disc 2 of American Acoustic is sad and plaintive.  The contribution of the Amperex-made tubes clearly in play.
• Certain sound effects, such as the rustling of curtains, on the blu-ray presentation of HBO’s  Rome series are extremely realistic.
• Although the sound stage is almost as good as it gets on my system, images are more diffuse and not quite as dense as with the all-Amperex 6922 PQ tube complement.
• Likewise, percussion is near reference level but not quite in the same league as the all-Amperex 6922 PQ presentation.

The Valvo 6922 is another first-tier dual triode in this tube family.  This particular combination definitely has the Amperex house sound but it’s leavened with some Teutonic coolness thanks to the Siemens-made Valvo’s that are in the mix. 

I would venture to guess that a set of Valvo 6922’s comprised solely of tubes made by either Amperex or Siemens might possess a character indistinguishable from those branded with their manufacturer’s own name.  But then, my experience with the Telefunken made PCC88’s and the PCC88’s made by Siemens might belie my previous comment. 

You never really know until you try them for yourself. 

The subject tubes under review are the Amperex 6922 PQ with the large O-ring getter.  They were all manufactured in the Amperex Hicksville, NY plant during the years 1961 and 1963 to 1965.  The 6922’s were purchased via auction from various sellers.  Although they may still be found today from vendors such as Tube World and Upscale Audio, they are rather expensive and average about $170 each.

Amperex (USA) 6922 PQ Line-Up                                                            Amperex (USA) 6922 PQ Front View
     

Amperex (USA) 6922 PQ Rear View                                                         Amperex (USA) 6922 PQ Large O-ring
     

 Amperex (USA) 6922 PQ Date Code
     

NB:  If you should click on any of these photographs, that will bring up the image in a separate window.  If you then click on the image once again while you're in the Photos section, it will allow you to view an even larger image so that photographic details become easier to view.  This holds true for almost all the images you'll find within these blog entries.

The associated tube complement in my c-j Premier 140 amplifier was the Russian-made Voskhod 6H30π-DR pulling duty as phase splitters and SED 6550C power tubes.  This configuration was highly complimentary and brought out the best in the Amperex 6922’s.

The previous small signal tubes were Lorenz PCC88, quite possibly my favorite all-around small signal tube in the Premier 16LS2 preamplifier and the Lorenz are second only to the Amperex pinch waist 6922 as my favorite input tube in the Premier 140.

Listening Impressions:

• The Narada album playlist I have on the Olive O3HD, via the Oppo BDP-95, revealed the classic Amperex smoothness of sound while maintaining superb clarity and inner detail with crisp transients.
• Bass response, aided and abetted by the recently re-introduced XLO Signature 5.1 speaker cables, is strong and macro-dynamics are reference level for my system.
• Percussion on HBO’s Rome series on blu-ray rivaled the Amperex pinch waist 6922 PQ and quite honestly, in a blind test (shudder), I would be hard-pressed to tell the two apart.
• The guitar work during HBO’s Boardwalk Empire intro via cable has first class clarity, spirit and emotion.
• Mid-treble is always comfortable and relaxing with excellent extension but never any edginess.
• The Four Seasons CD featuring Trevor Pinnock and the English Concert on the Archiv label, played on the Music Hall CD-25, is beautifully musical and the solo and massed violins are glorious.
• The cymbal work on Reference Recordings From the Age of Swing CD is feathery.
• Details are reference level, allowing me to hear how the XLO Signature 1.1 interconnects on the BDP-95 are a little smoother sounding versus the Nordost Red Dawn Rev II interconnects on the Music Hall CD-25. 
• The counterpoint on Columbia Masterworks The Japanese Album CD track entitled “Chidori No Kyoku” is clearly revealed.
• Images are larger than those cast by the Lorenz PCC88 with a strong central image presence.  The sound stage, at times, extends well beyond the speaker boundaries and projects into the listening room a squared-off (as opposed to triangular) reproduction of the venue.

Purple prose aside, the Amperex (USA) 6922 PQ are top flight tubes in this class.  Although they are very expensive, if you can swing it financially, I don’t think you’ll be disappointed.